Indoor Windowsill Plants

Useful and Fragrant Herbs

• Herbs can be sources of cuttings for your cooking and provide aromatic foliage that scents the air when handled. Many herbs have ornamental foliage and flowers; those plants include rosemary (Rosmarinus officinalis), which is hardy in U.S. Department of Agriculture plant hardiness zones 8 through 10, and basil (Ocimum basilicum, USDA zones 9 through 11). Grow herbs on the sill of a sunny, south-facing window, and supplement light from it with fluorescent fixtures if necessary. Move the herbs' pots one-quarter turn each week to prevent lopsided growth in the plants. When the plants' top 1 inch of soil is dry, water it until water flows out the pots' bottom drainage holes. Herbs can grow indoors year-round, or they can spend winter indoors and be moved outdoors in spring when the danger of frost is gone.

Flowering Bulbs

• Especially in late winter and early spring, flowering bulbs such as daffodils (Narcissus spp., USDA zones 3b through 10) and Giant Darwin Hybrid Tulips (Tulipa Darwin hybrid, USDA zones 3 through 7) brighten indoor windowsills. Bulbs used for forced blooming indoors should be regarded as expendable because they use most of their stored energy in one season's bloom and cannot replenish it. Choose large bulbs and a potting mixture that is three parts garden loam, one part sand and two parts peat moss. Use a 6-inch-wide, clean pots with bottom drainage holes. In October, place the bulbs close together in the pots, planting six bulbs per pot. The noses, or tops, of the bulbs should be above the potting mixture's surface. Water the potting mixture until water flows through the pots' drainage holes. Put the pots in a dark place that is 35 to 48 degrees Fahrenheit, and leave them there for eight to 16 weeks, keeping the potting mixture moist. Setting the potted bulbs on a sunny windowsill in late December should result in blooms about six to eight weeks later.

Succulent Varieties

• A west- or south-facing windowsill is necessary for sun-loving, water-storing succulent plants such as crown of thorns (Euphorbia milii, USDA zones 8 through 11), which blooms in spring and summer. Like most succulent Euphorbia plants, crown of thorns has white sap that can irritate skin, eyes and mucous membranes. Wear heavy-duty, waterproof gloves when handling crown of thorns and other Euphorbia plants; the gloves will protect you from the sap as well as crown of thorns' thorns. Also, crown of thorns and other Euphorbia plants shouldn't be eaten. Another succulent, the kalanchoe houseplant (Kalanchoe blossfeldiana, USDA zones 10 through 12), accepts bright indirect light or full sun, making it suitable for east-facing, south-facing and west-facing windowsills. Kalanchoe has showy clusters of pink, yellow, orange or red flowers. Both kalanchoe and crown of thorns need a cactus potting mix. Water their potting mix thoroughly when its top 2 inches become dry, using enough water so some of it exits through the pots' bottom drainage holes.

Bonsai Subjects

• Bonsai plants can grow successfully on west- or south-facing windowsills. These artificially dwarfed plants are labor-intensive to train and maintain. The reduced soil volume around the roots of bonsai plants doesn't allow much margin of error in watering them. Check your bonsai plants every day for their watering needs, which vary with weather conditions, time of year and plant species. During sunny, summer weather a plant may need watering twice each day, and in the winter several days may go by without watering being necessary. Rotate bonsai plants' pots one-quarter turn each week so the plants grow evenly and straight.